Petra Diamonds has announced plans to construct a new processing plant at its Cullinan diamond mine in Gauteng province, South Arica, 40 km east of Pretoria. Throughput capacity will be 6 million metric tons per year (mt/y). Capital cost of the project is estimated at about R1,650 million ($142.8 million).
The Cullinan mine has been in production since 1902 and is known for consistently producing large, high-value diamonds, including the famous 3,106-carat Cullinan diamond, the largest gem diamond ever recovered. The current plant was originally commissioned in 1947.
Petra expects the new plant to improve recovery of the full spectrum of diamonds, thereby increasing the volume of stones recovered and better protecting large stones from breakage. The plant also will improve the efficiency of material flow, thereby significantly lowering operating costs.
The plant will incorporate autogenous milling and high-pressure grinding rolls, which will provide gentler liberation than the crushing and high-impact cone crushing processes employed in the current plant. XRF X-ray technology will replace conventional dense media separation to treat coarser >12-mm material.
In addition to the benefits to large stone recoveries, Petra expects the improved diamond liberation technologies to lead to an improvement in the overall grade achieved at Cullinan.
The new plant will reduce the processing footprint at Cullinan from about 26 ha to 5 ha, with an associated reduction of engineering infrastructure, including an expected reduction in the number of conveyor belts from 151, spanning 15 km, to 22, spanning 3 km. Operating efficiencies and security improvements also will be driven by increased automation, reduced tons in circulation and improved energy efficiencies.
MDM Engineering will execute the bulk of the project work for the new Cullinan plant. Petra expects the plant to be commissioned and fully operational by mid-year 2017. Day-to-day operations at Cullinan will continue as usual while the new plant is being constructed.
Cullinan has a world-class diamond resource of 199.6 million carats, including 17.2 million carats in tailings. Petra is capitalizing on this resource by undertaking an expansion program to take annual production to about 2.2 million carats by its 2019 fiscal year. Cullinan produced 823,619 carats in the company’s 2014 fiscal year to June 30, 2014.
Mining at Cullinan is by underground block caving. The current mine plan has a life of 16 years, but the resources at the mine indicate that actual mine life could be in excess of 50 years.
The expansion now in progress is establishing a new block cave on the western side of the Cullinan orebody.
The Cullinan mine is owned 74% by Petra Diamonds, 14% by Thembinkosi Mining Investments (Pty) Ltd., and 12% by Petra Diamond Employee Share Trust.